Method and means for carburizing iron, steel, and alloys thereof



A. J. P. BERTSCHY. METHOD AND MEANS FOR CARBURIZING IRON, STEEL, AND.ALLOYS THEREOF.

APPLICATION FILED JAN- 3. I920.

Patented Mar. 7, 1922,

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A.QJ-RBERTSCHY1 mzL WI Emma:

carburizing process, may be produced in UNITED STATES PATENT OFFICE.

ADOLPH 3'. 1. BERTSCHY, 0F OMAHA, NEBRASKA.

METHOD AND MEANS FOR GARBURIZING IRON, STEEL, AND ALLOYS THEREOF.

Patented. Mar. '7, 1922.

Application filed January 3, 1920. Serial No. 3%,147.

To all whom it may concern:

Be it known that I, AnoLrH J. P. Bnn'rsonv, a citizen of the United States, and a resident of Omaha, in the county of Douglas and State of Nebraska, have invented certain new and useful Improvements in Methods and Means for Carburizing Iron, Steel, and Alloys Thereof, of which the following is a specification.

My invention relates to case-carburizing of iron, steel and alloys thereof, or to methods and apparatus for increasing the carbon content of such materials by treatment at temperatures below the melting-point thereof. It is the object of my invention to provide simple and commercially practicable methods and apparatus for carburizing materials of the class mentioned, whereby a very rapid and uniform penetration of the added carbon may be attained, and wherein it is unnecessary to provide for movement pr agitation of the treated articles during the carburizing operation.

In the accompanying drawing 1 have illustrated diagrammatically an apparatus suitable for carrying out my carburizing process, the figure being a partial longitudinal section of the apparatus.

Referring first to the illustrated a paratus, there is indicated a furnace 1 W ich will be understood to be heated by any suitable controllable means, such as gas, whereby to maintain the required temperature within the retort 2 in which are placed the articles A to be carburized. The retort 2 extends horizontally through the furnace, and is closed at the rear and front ends, respectively by members 3 'and 4:, either or both of which may be removable. members 3 and 1 are preferably fitted so that a substantially gas-tight joint is provided around them} enabling the maintenance of some pressure within the retort, although the use of pressure is not an essential of my and satisfactory work a retort having one end, or a substantial part thereof, open to atmosphere. Somewhat more economical control 'of the process is attained, however, in the closed retort. The front or door-member 4 of the retort is shown as provided with an o ening throu h which a thermocouple en- 0 osing tube 5 1s extended into the retort, the thermo-couple being connected with-a suitably calibrated amuneter 6 for indicating temperatures attained within the retort.

Said

'carburizing materials employed are mainly at normal or ordinary ator entirely liquid and provision is mospheric temperatures, made for supplying such materials to the feed-pipe 10 as follows: A portion of the pipe is enclosed by a jacket 12, forming around the pipe a chamber 13 through which heating or cooling media may be circulated, through pipes 14 and 15 connecting with the jacket. The portion of the feed-pipe within the jacket forms a multiple header, being branched therein to connect with a plurality of pipes 16, shown as extending vertically through the jacket. Each of said pipes 16 has a control-valve 17, and may also be provided with sight-feeding devices 18, through which the dropping of liquids fed through them may be observed. To each of the pipes 16 there is connected a reservoir 19, only one of which is shown completein the drawing, but all of which will be understood to be alike. To the upper closed end of the reservoir there is connected a pipe 20 through which the reservoir is filled, said pipe having a valve or cook 21 which may be opened or closed as required. To said upper closed end of the reservoir there is also connected a pipe 22 through which air-pressure may be supplied should it be desired to force-feed the material from the reservoir to the pipe 10. The pipe 22 has a lateral branch 23 connecting with a pressure-gage 24 and a blow-off peacock 25.

In the use of the described a paratus to carry out my process, the artic es A to be treated are placed within the retort preferably being arranged therein with substantial uniformity and held apart by suitable spacing members B. To secure uniform results, none of the articles should be placed in immediate proximity to the end of the feedpipe, and all of the articles should be in portions of the retort which experience has shown to be capable of being maintained by the furnace at substantially uniform temperature throughout. In general, better rially from results are attained when 'the space within the retort is well filled with the treated articles than when said space is only partly filled; providing, of course, that the articles themselves should be slightly separated from each other, and excluding from consideration the space immediately adjacent to the end of the feed-pipe, as well as any portion or portions of the retort which are found to be heated by the furnace abnormally, or to temperatures differing mate the remaining major portion thereof.

The temperatures to which the retort is heated during the carburizing operation may be varied according to the results'desired, the extreme range being from 1400 F. to 1900 F, with a preference in most instances for temperatures ranging from 1700 F. to 1800 F. The lower limit of temperature appears to be the critical temperature of the material, at which the contained carbon enters into solid solution, and to which the steel must be heated in order to effect hardening thereof upon quenching. Tn general,the higher the temperatures the more rapidly the carburizing effects are produced, and the maximum limits of temperature are those which may be attained-with the particular material operated upon, without injury thereto.

The particular characteristic of the apparatus employed for carrying out my process,

lies in the provision of means for feeding into the retort, with substantial continuity throughout the carburizing period, of carbonaceous materials which are liquid at normalatmospheric temperatures, said materials being fed directly to the retort so as to either enter the same while in the liquid form or to become vaporized only immediately preceding, and substantially upon, their entry into the retort-chamber.

My process is especially characterized by the substantially continuous feeding to the retort, during the carburizing period, of normally liquid carbonaceous material capable .of being decomposed at the temperatures maintained within the retort, and the controlling of the rates of feed and escape, and of the maintained temperatures of the retort, such as to establish therein around the treated articles a zone of substantially uniform reaction in which the changes being undergone by the material are favorable to "the release therefrom of carbon in such a form or state as to penetrate and combine with the metal in the articles'being treated.

The carbonaceous materials suitable for use in the process appear to be any of the higher homologues of the several hydrocarbon series, such as of the paraflin, olefin, acetylene, terpene, benzene, naphthalene, anthracene, or other series. In actual practice I have employed principally petroleum and the various refined products thereof, and have obtained satisfactory results from the use of such materials, ranging in composition and density from crude oil through the various refined products to kerosene. Besides the usual factors of time andtemperature, which control carburizing in other processes, in my process the character of the case obtained upon the treated articles, and the depth of penetration thereof, are varied according to (a) the kind or density of the oil used, (6) the quantity fed per unit of time and proportional to the transverse sectional area of the retort through which the decomposing vapors pass, and (c) the size of the vent through which the evolved gaseous products escape from the retort. The latter factor, when the vent is restricted, ma result, of course, in the building up of s i ht pressure within the retort. Different liqulds, such as oils of different densities, may be placed in the several reservoirs 19, and fed to the pipe 10 either simultaneously or alter natively; or oil of the same kind may be placed in two or more of the reservoirs and fed therefrom alternately, the feed from one being started as the other becomes empty, so as to maintain the continuity of feed to the pipe 10, without interruption due to necessity of refilling the reservoir first used. When using the lighter and more highly refined oils, a cooling medium such as water may be circulated through the jacket-space 13, to prevent heating of the feed-pipe 10 such as might result in vaporization of the oil prior to its entering the retort-chamber.

For heavy oils or greases, the flow thereof may be facilitated by circulating a heating medium through the jacket-space The feeding of the oil into the retort is preferably commenced when the temperature of the latter reaches the lower limit of the effective range, and is continued substantially throughout the period during which the articles are treated. The decomposition of the higher or complex hydrocarbons under the heat to which the same are subject while passing through the retort, results in the formation therein of soot-like particles and flakes, portions of which pass off through.

the vent, together with gaseous products,

and the remaining portions are deposited in the retort in the form of a loose, spongy mass. In general, larger amounts of the spongy deposit are formed with heavier oils and with higher temperatures, than with lighter or more refined oils and lower temduce a scanty deposit of the spongy material,

as with heavier oils which cause a profuse deposit of such material. It should be different portions of the retort.

at the mouth of the retort.

incense understood, however, that it is desirable and perhaps necessary to have in the retort a certain amount of the spongy carbon, as it cake which can only be removed from the retort with some dilllculty, by forcibly scraping the same off the walls. It appears further that after the described hardening of the 'deposit has occurred, no effective carburizing action is attained in the retort until the spongy deposit begins to be built up by the feeding of fresh oil at a suitable rate. Another viewpoint as to the spongy carbon deposit, is to regard the same as an index for thereaction Zone in which the most effective carburizing action is attained. Thus, in a retort of a given length, in which the oil is fed at one end and the gaseous products discharged the other end, should the rate of feed of the oil be made such that the cracking of the heavier hydrocarbons is completed and the ultimate products of the reaction attained, or a. state of equilibrium reached for the particular temperature, such that there is no deposit of the spongy carbon near the discharging end of the retort, then it is apt to be found that articles disposed in the retort near the discharge end are not carburized uniformly with articles disposed in the zone of deposit of the spongy material. In a retort having an open discharge end,

so that the interior may be directly observed,

the character of the reaction may be judged by the appearance of the materials in the JVith a proper rate of feed, air is efiectively expelled from the retort by the heavy vapors of the oil, which, of course, become ignited and burn as they escape into air at the mouth of the retort. The formation of the sooty particles and their deposit upon the walls of the retort and upon the articles being treated can be clearly seen, and incandescent particles of carbon may be noted in the flame Thin streams of blue-white vapor are seen to rise from the spongy carbon deposit, and the evolution thereof may be greatly accelerated by mechanically stirring thedeposit. With a substantially closed retort, having merely a venttube for the escape of the gaseous products, as in the illustrated apparatus, the character of the reaction occurring at any time may be judged by'the appearance of the escaping vapors, or by the appearance of the flame produced by ignition thereof. A proper rate of feed of the carburizing material to the retort is indicated in this case by the appearance of a moderate amount of sooty particles at the end of the vent-tube, giving the escaping material a black smoky appearance, and the flame when ignited at the end of the vent-tube has a. central reddish luminous cone in which the larger carbon particles form bright points, while the outer portions of the flame are noticeably bluishwhite. An excessive feed is indicated by a brown color of the unignited escaping material at the vent, and insufiicient feed is indicated by the disappearance or scantiness of the carbon-particles.

The control of the reactions occurring in the retort is closely comparable to thatemployed in the cracking of petroleum and the like, for the production of gasolene, benzene, toluene, xylene, etc. Investigations in this art have shown that atany particular temperature and pressure, a mixture of hydrocarbons, or of hydrocarbons with free hydrogen or carbon, or both, tends to reach a state of equilibruim at which definite quantities of the various materials will be present. A certain time, however, is required for the completion of the reaction, so that the state of'equilibrium will not be attained if, within less than the time required for completion of the reaction, fresh materials are added or portions of the materials withdrawn from the reaction zone. 'In consequence of the time-factor involved in the reaching of an equilibrium, it is possible to vary the proportions of the resultant products of the cracking of higher hydrocarbons by varying: the

rate of feed, while the conditions of pressure and temperature are kept constant.

Applying the same reasoning to the decomposition of the higher hydrocarbons as employed in my carburizing process, it will be seen that by similar variation of the conditions, principally temperature and rate of feed, a zone of reaction may be established and maintained substantially throughout the retort, wherein the resultant products are those which most highly favor the release ofcarbon in such a form or state as topenetrate and combine with the iron or ferric alloy.'

I am aware'that certain hydrocarbons have been employed in carburizing processes heretofore known, but in all such processes wherein the hydrocarbon is fed continuously during the carburizing operation, a fixed and stabilized gas, generated outside of the retort has been employed. Ethane, methane, acetylene, ethylene, and other fixed hydrocarbon gases, existing as such at ordinary temperatures, are known to be capable of effecting more or'less carburization of iron when maintained in the presence thereof at suitable temperatures. Ethylene, in fact,

, iaoacse mercial case-hardened work, it is desirable the latter at the surface.

that the-case atthe surface should have a carbon-contentnot exceeding eutectic, and that there should be considerable penetration with a uniform and gradual reduction of the carbon-content from the surface inward.

' Carburization of this character is readily attained by my process, and is effected with remarkable rapidity. With specimens of soft steel, of 15% to 2% carbon-content, I have been able to carburize same to a depth of inch or more by treatment for two hours at temperatures ranging around 1700 F., the

case obtained having a carbon-content be tween .45% and eutectic, and not exceeding Moreover, the depth of penetration obtained is very nearly proportional to the length of the period of treatment, the penetration curve showing a gradual rise, and the rate not showing the marked slowing with increased penetration common to most carburizing processes. Carburizing by my process is not appreciably retarded by the presence of metals commonly alloyed with steel, such as chromium, vanadium, tungsten, manganese, or nickel. Nickel, for example, is shown to greatly retard carburization by ordinary methods, but with my process the carburization of nickelsteel may be effected at substantially the same rate as ordinary unalloyed or plain carbon steel.

As an example of the remarkable penetrae tive power of the carburizing substance or substances produced in carrying out my process, I ma-yment-ion instances in which two plates were secured together by riveting, in order to prevent carburizing of their adjoining faces. Aftertreatment of the plates thus secured ,together, examination thereof showed that carburization had been effected around the rivets for a considerable distance below the outer surface of the plates, the carburizing material apparently having penetrated the microscopic joint-space left after the upsetting and heading of the rivets. In the same examples,- although the plates were held together by rivets and their edges cemented together, there was considerable penetration through the joint and into the back faces of the pairs of plates. this it will be seen that agitation of the'articles within the retort, or special arrangement From what the material or materials 2110, me being formed during the cracking and decomposition of the higher or complex hydrocarbons in carrying out my process, produce the carburizingeffects attained by the process. lit is certain, however, that the carb'u' rizing agent or agents are themselves hydrocarbons, since no other class of materials is present. It is fairly certain also that the effective agent or agents are not mere endproducts of hydrocarbon decomposition, or the lower members of the hydrocarbon series, such as ethane, methane, ethylene, acetylene, etc., since these agents, by themselves or in any known combinations, cannot be made to effect the results attained by my process. It appears probable that the effective agent or agents are intermediate products, resulting from the progressive reduction of the higher and more complex hydrocarbons, and formed t-ransitorily in the'reactions tending to produce a state of equilibrium at the tempera-- tures employed in the process. It is noted that the end-products or equilibrium products resulting from continued treatment of the higher hydrocarbons at the temperatures employed in the process, are free carbon, hydrogen, and the fixed gases which constitute the lowestmembers of the hydrocarbon series, particularly of the parafiins, olefins and acetylenes. It seems probable that the effective carburizing agent or'agents comprise a hydrocarbon vapor of such composi tion that under the conditions present in carrying out the process the material has an extraordinary capability of penetrating the \metal; that the said hydrocarbon, being unstable at the temperatures employed, undergoes a decomposition while in intimate or molecular contact, with the metal, the decom position being of such a nature as to release carbon in a nascent or infra-molecular state, so that the released carbon unites with the metal and is retained thereby. The foregoing is offered merely as a working hypothesis as to the nature of the reactions occurring, but is borne out by all experimental and other datanow available.

An interesting indication of the nature of the reactions which occur in the retort during the carburizing process, is offered by the pyrometer readings when regulating the heat of the furnace to bring the same up or down to the temperature desired to be maintained, or when varying the rate of feeding of oil to the retort. At temperature below about 1780 F., other conditions being uniform, increasing the rate of oil-feed causes a marked lowering of temperature in the retort, and decrease of vrate of feed causes an increase of-temperature, so that apparently the reactions occurring are principally endothermic in character. It appears further that-at temperatures approximaing 1800 F the reactions tend to become exothermic.

This is made evident'by maintaining a uniform rate of oil-feed, and regulating the heating devices of'the furnace so as to pro duce a gradual increase of temperature approaching the temperature last mentioned. At about 180() the rate of increase will be noticeably accelerated, and upon reaching a temperature of 25 to 30 degrees higher said temperature will be maintained even though the furnace heating devices be shut down to a point which previously would serve only to maintain a temperature of the retort 100 or more degrees lower. In fact, after once bringing the retort-temperature up to the exothermic phase, it is sometimes difiicult to secure a lowering of the temperature except by stopping the oil feed untilthe lowering is effected.

) Now, having described my invention, what I claim and desire to secure by Letters Patent is:

1. The method of case-carburizing, con-- sisting in heating the treated articles to and maintaining the same at a temperature above the critical temperature for hardening the material; and supplying with substantial continuity, so as to maintain about the heated articles a nearly uniform atmosphere thereof, a relatively complex hydrocarbon unstable at the maintained temperature of the articles.

2. The method of case-carburizing articles of steel, consisting in heating the same above the critical hardening temperature of the steel, in the presence of complex hydrocarbons which are unstable at the maintained temperature, whereby said hydrocarbons undergo constant decomposition of a character tending to free carbon therefrom, and supplying the hydrocarbons at a controlled rate, whereby to maintain a substantially constant reaction zone about the articles.

3. The method of case-carburizing articles of iron and steel, consisting in heating and maintaining the same at temperatures ranging upward from the critical temperature of the material, in a constantly replenished atmosphere consisting principally of intermediate decomposition products of complex higher hydrocarbons.

4E. The method of case-carburizing articles of iron, steel and alloys thereof, consisting in heating the articles 1n an atmosphere consisting principally of petroleum decomposition products, and discharging said decomposition prolucts from the reaction zone containing the treated articles, at a rate such as to substantially exclude from said zone the decomposition end-products other than carbon.

5. The method of carburizing articles of iron, steel and alloys thereof; consisting in decomposing normally liquid hydrocarbons by abruptly subjecting the same to temperatures high enough to release carbon therefrom, placing the articles to be .carburized in the zone of said decomposition, and controlling the rate of feed of the hydrocarbons to andof escape of the decomposition products from said zone so as to maintain a substantially constant reaction therein.

6. The method of carburizing articles of iron, steel and alloys thereof, consisting in passing normally liquid petroleum products abruptly into a zone of high temperatures such as to decompose and release carbon therefrom, placing the articles to be carburized in the zone of reaction in Which carbon is being released, and maintaining a substantially constant rate of feed and escape of the materials to and from said zone of reaction.

7. The method of carburizing articles of iron, steel and alloys thereof, consisting in heating the articles to carburizing temperatures in a current of relatively complex hydrocarbons unstable at the maintained temperature, and so controlling the rate of flow of said current as to maintain about the articles a reaction zone in which the decomposition products are intermediate the initial hydrocarbons and the end-products of decomposition thereof at the maintained temperatures and pressures.

8. The method of carburizing articles of iron, steel and alloys thereof, consisting in heating the articles to carburizing temperatures in a current of normally liquid petroleum products which are unstable at the maintained temperature, and so controlling the rate of flow of said current as tomaintain about the articles a substantially constant reaction zone containing decomposition products intermediate the initial and end-products of decomposition of the material at the maintained temperatures and pressures.

' A. J. P. BERTSCHY. 

